Effects of cytochalasin B and enucleation on EGF receptor down regulation.

The loss of epidermal growth factor (EGF) binding activity on cultured murine 3T3 cells exposed to EGF (EGF receptor down regulation) was determined in colchicine treated cells, cytochalasin B treated cells, and untreated cells. Neither colchicine nor cytochalasin B altered the affinity of the receptor for EGF, but colchicine decreased maximal EGF binding activity by 20%. The maximal extent of EGF receptor down regulation was similar in colchicine treated cells and cytochalasin B treated cells, but the rate of receptor down regulation was higher in cytochalasin B treated cells. Cytoplasts produced by subjecting cytochalasin B treated cells adhering to the substratum to centrifugal force responded to EGF with nearly normal down regulation kinetics. The results suggest that the cytoskeleton is not obligatorily involved in EGF-induced EGF receptor down regulation.